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The hints are expected to get a bit more complicated, so
move them to a separate file instead of an inner class.

There is no loss in test coverage, but I am planning to
add separate unittests file in a subsequent CL.

Change-Id: I8c94ffc93de2e4b0e7e88c9c50344f499ab03cf3
Bug: 856243
Reviewed-on: https://chromium-review.googlesource.com/1116518Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570845}